1. Field of the Invention
The present invention pertains generally to flexible inner members rotatably disposed within angled outer tubular members of rotary surgical tissue cutting instruments wherein the inner member has a flexible region to transmit torque while conforming to the angled configuration of the outer tubular member. More particularly, the present invention pertains to flexible inner members of angled rotary tissue cutting instruments wherein the flexible region comprises a labyrinthine cut formed in a tubular body of the inner member.
2. Brief Discussion of the Related Art
Angled rotary tissue cutting instruments have become widely accepted for use in various surgical procedures to cut anatomical tissue at a surgical site within a patient's body. Angled rotary tissue cutting instruments typically comprise an elongate angled outer tubular member and an elongate flexible inner tubular member rotatably disposed within the angled outer tubular member. A cutting element at a distal end of the inner member is exposed from an opening at a distal end of the outer member to cut anatomical tissue at the surgical site when the inner member is rotated within the outer member. The inner member is ordinarily rotated within the outer member via a powered surgical handpiece coupled to proximal ends of the outer and inner members, with the handpiece being maintained externally of the patient's body. The outer tubular member has one or more angled, curved or bent regions along its length to provide an angled configuration that facilitates positioning of the cutting element at the surgical site when the instrument is introduced in the patient's body, and particularly when the instrument is introduced through a narrow or small size, natural or artificially created entry opening in the patient's body. The inner tubular member is provided with one or more flexible regions to reside within the one or more angled, curved or bent regions of the outer member for transmitting torque to rotate the cutting element while conforming to the angled configuration of the outer member. The angled configuration of the outer member is particularly beneficial in facilitating positioning of the cutting element at the surgical site where there is a non-straight path in the body from the entry opening to the surgical site. In such cases, angled rotary tissue cutting instruments are usually better suited to access the surgical site more easily and quickly, and with less trauma to the patient, than are rotary tissue cutting instruments in which the outer tubular member is longitudinally straight. In many surgical procedures performed using rotary tissue cutting instruments, the internal lumen of the inner tubular member is used to transmit suction to the surgical site to aspirate anatomical tissue and/or fluid through the inner member. In addition, an annular gap or clearance between the internal diameter of the outer member and the external diameter of the inner member is commonly used as an irrigation passage to supply irrigation fluid to the surgical site.
One design advantage in rotary tissue cutting instruments is to minimize the external diametric size of the outer member to allow introduction of the instrument in the patient's body through entry openings as small as possible in size and/or to facilitate advancement of the instrument to the surgical site with as little trauma as possible to the patient. Another design advantage in rotary tissue cutting instruments is to maximize the internal diameter of the inner tubular member so that aspiration of tissue and/or fluid through the inner member can be accomplished with greater efficiency and with less risk of clogging. Yet a further design advantage in rotary tissue cutting instruments is to maintain an appropriate annular clearance between the internal diameter of the outer tubular member and the external diameter of the inner member to avoid jamming of the instrument and/or to provide efficient flow of irrigation fluid between the outer and inner members. In angled rotary tissue cutting instruments, it would also be a design advantage to minimize the number of structural components or parts required for the flexible region of the inner member, thereby reducing manufacturing and material costs, as well as reducing the risk of operational problems arising from structural complexity and/or multiple structural components. The foregoing design advantages must necessarily be balanced against the need to maintain sufficient strength and rigidity in the flexible inner members of angled rotary tissue cutting instruments when transmitting torque via the flexible regions, particularly considering that angled rotary tissue cutting instruments must oftentimes be designed to operate at high rotational speeds and to withstand the forces imposed when cutting very hard or tenacious anatomical tissue.
Various designs previously proposed for the flexible regions in the inner members of angled rotary tissue cutting instruments have limited the extent to which the aforementioned design advantages can be optimized in angled rotary tissue cutting instruments. Some of the deficiencies associated with prior designs proposed for the flexible regions in the inner members of angled rotary tissue cutting instruments include increased radial thickness of the annular wall of the inner tubular member along the flexible region resulting in a larger external diameter and/or smaller internal diameter for the inner member, structural complexity and/or the need for multiple assembled structural parts to form the flexible region, constriction of the internal diameter of the flexible region when transmitting torque within an angled region of the outer tubular member, longitudinal stretching of the flexible region, and insufficient strength and rigidity in the flexible region limiting the range of bend angles over which the flexible region is able to effectively transmit torque. Designs for the flexible regions of inner tubular members of angled rotary tissue cutting instruments that result in the inner tubular member being of larger external diametric size normally require that the angled outer tubular member be of larger external diametric size in order to rotatably receive the inner member while maintaining the appropriate annular clearance between the outer and inner members. Designs for the flexible regions of inner tubular members of angled rotary tissue cutting instruments that result in the inner tubular member having a smaller internal diameter or that result in constriction of the internal diameter will typically have a negative impact on the ability to aspirate tissue and/or fluid through the inner tubular member. Designs for the flexible regions of inner tubular members of angled rotary tissue cutting instruments that involve structural complexity and/or multiple assembled structural parts generally result in the inner tubular member being of higher cost and at increased risk of operational problems. Operational problems are also more likely to occur in inner tubular members of angled rotary tissue cutting instruments in which the design for the flexible region in the inner member makes the flexible region prone to longitudinal stretching.
In some flexible inner tubular members of angled rotary tissue cutting instruments, the flexible regions are formed of a plurality of concentric spirals, typically an inner spiral, a middle spiral and an outer spiral attached to one another at their ends. Each spiral is formed by winding a flat strip of material, with alternating spirals being wound in opposite rotational directions about a central longitudinal axis of the inner member as represented by U.S. Pat. No. 4,646,738 to Trott, U.S. Pat. No. 5,286,253 to Fucci and U.S. Pat. No. 5,540,708 to Lim et al. It has also been proposed to provide shafts having flexible regions made up of concentric coils of wound wire of circular cross-section, rather than wound flat strips of material, as represented by U.S. Pat. No. 5,437,630 to Daniel et al and U.S. Pat. No. 5,529,580 to Kusunoki et al and by German Patent DE 3828478 A1. The radial dimension or thickness of the annular wall of a flexible region comprised of multiple concentric spirals or coils tends to be substantial since it includes the individual thickness of each spiral or coil. Flexible regions of this type tend to result in flexible inner tubular members of larger external diametric sizes requiring diametrically larger outer tubular members, and/or of smaller internal diameters leading to reduced aspiration capability. In addition, flexible inner tubular members having these types of flexible regions will ordinarily be associated with higher material costs due to the multiple structural components involved and with higher manufacturing costs associated with producing and assembling the different structural components. The risk of operational problems may be greater due to the presence of multiple structural components and increased structural complexity, and the securement or attachment sites for the multiple spirals or coils present the potential for structural failure.
Another design approach for the flexible regions in the flexible inner tubular members of angled rotary tissue cutting instruments involves a single continuous spiral or helical cut formed in an inner tube, and one or more layers of spiral wrap disposed over the cut region of the inner tube as represented by U.S. Pat. No. 6,533,749 B1 to Mitusina et al and U.S. Pat. No. 6,656,195 B2 to Peters et al, and by U.S. Patent Application Publication No. US2005/0090849 A1 to Adams. The one or more layers of spiral wrap are each formed by winding a flat strip of material over the cut region in the inner tube and attaching the ends of the strip to the tube. The helical cut and the one or more layers of spiral wrap are arranged so that their rotational direction or turn about a central longitudinal axis of the inner member alternate in opposite directions. The Peters et al patent discloses the helical cut in the inner tube as having a dovetail pattern. The extent to which it is possible to minimize the radial dimension or thickness of the annular wall of a flexible region comprised of an inner tube and one or more layers of spiral wrap over a cut region of the tube is limited by the fact that the wall thickness of the inner tube and the thickness of each layer of spiral wrap contribute cumulatively to the radial dimension of the annular wall formed by the flexible region. Furthermore, the inner tube and each spiral wrap are separate structural components assembled during manufacture, giving rise to issues of increased cost and structural complexity.
U.S. Pat. No. 7,338,495 B2 to Adams is an example of a flexible region in a flexible inner tubular member of an angled rotary surgical cutting instrument formed of a helical cut in an inner tube, a layer of adhesive disposed over the cut region of the inner tube, and a heat shrunk sleeve disposed over the cut region of the inner tube and being bonded thereto by the adhesive. The helical cut is formed in the inner tube in a stepped pattern. Again, the radial thickness of the annular wall formed by the flexible region is made up of the individual thicknesses of the inner tube wall, the adhesive layer, and the wall of the sleeve. The flexible region requires multiple parts or materials in addition to the inner tube, and is still somewhat complicated from a manufacturing standpoint.
Flexible regions have also been provided in the inner tubular members of angled rotary tissue cutting instruments by forming disconnected slots or openings in an inner tube as illustrated by U.S. Pat. No. 5,152,744, U.S. Pat. No. 5,322,505 and U.S. Pat. No. 5,510,070 to Krause et al, U.S. Pat. No. 5,620,415 to Lucey et al, and U.S. Pat. No. 5,620,447 to Smith et al. Each slot is filled with a pliable material in a multi-step process carried out after the slots are formed. The preferred slot configuration described in the Krause et al, Lucey et al and Smith et al patents involves circumferentially discontinuous slots disposed in parallel spaced relation, the slots being arranged perpendicular to the longitudinal axis of the inner tube.
U.S. Pat. No. 6,053,922 to Krause et al pertains to a flexible shaft for reaming the medullary space in bones. In contrast to the flexible inner members of angled rotary tissue cutting instruments, the flexible shaft of Krause et al '922 is not designed to be rotatably disposed within a rigid outer tubular member, and is thusly not subject to the same design considerations as the inner members of rotary tissue cutting instruments and of angled rotary tissue cutting instruments in particular. In further distinction to the flexible inner tubular members of angled rotary tissue cutting instruments, the flexible shaft of Krause et al '922 is said to be an elongated tubular member of substantial wall thickness. A flexible inner tubular member of substantial wall thickness would be undesirable in an angled rotary tissue cutting instrument because it would result in a reduction in the internal diameter of the inner member, which would reduce aspiration capability, and/or it would require an outer member of larger external diameter to accommodate the inner member, which would require larger size entry openings in the patient's body for introduction of the instrument. The tubular member of Krause et al '922 comprises a slot, said to be of substantial width, extending spirally around the tubular member but in an undulating or serpentine pattern that forms complementary, mating interlocking shaped members in the tubular member that Krause et al '922 relies on to transmit torque.
Despite the numerous different design approaches previously proposed for the flexible inner members of angled rotary tissue cutting instruments, it was not recognized until the present invention that a flexible region comprising a labyrinthine cut formed in a tubular body of the inner member would provide numerous design advantages, including the advantages of design simplicity, eliminating the need for the flexible region to include an additional structure or layer of material over the cut region of the tubular body or within the cuts themselves, appropriate rigidity and torsional strength, resistance to stretching in the longitudinal axial direction of the inner member, preservation of the integrity of the internal diameter of the inner member, and the capability to transmit torque within angled outer tubular members having a broad range of bend angles.